When previtamin D 2 (which is identical to previtamin D3, p. 1478, except for the R-group) is isolated and irradiated, ergosterol is obtained along with a stereoisomer, lumisterol. The origin of lumisterol is to be explained mechanistically. Concept introduction: Electrocyclic reactions are a pericyclic reaction which occur intramolecularly. These reactions will result in the formation of ring compounds under the influence of heat or light. Notably, in this process one new sigma bond is formed and one old π-bond is consumed. Intriguingly, the reverse ring opening electrocyclic reaction can also be possible to occur under the same reaction mechanism but in reverse manner. In phase orbital overlap results in symmetry allowed electrocyclic reactions. Selection rules of electrocyclic reactions are; No. of electrons Activation mode Stereochemistry of rotation 4n Thermal Photochemical Con Dis 4n + 2 Thermal Photochemical Dis Con

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Chapter 28, Problem 28.25P

Interpretation Introduction

Interpretation:

When previtamin D₂ (which is identical to previtamin D3, p. 1478, except for the R-group) is isolated and irradiated, ergosterol is obtained along with a stereoisomer, lumisterol. The origin of lumisterol is to be explained mechanistically.

Concept introduction:

Electrocyclic reactions are a pericyclic reaction which occur intramolecularly. These reactions will result in the formation of ring compounds under the influence of heat or light. Notably, in this process one new sigma bond is formed and one old π-bond is consumed. Intriguingly, the reverse ring opening electrocyclic reaction can also be possible to occur under the same reaction mechanism but in reverse manner. In phase orbital overlap results in symmetry allowed electrocyclic reactions. Selection rules of electrocyclic reactions are;

No. of electrons Activation mode Stereochemistry of rotation

4n Thermal
Photochemical Con
Dis

4n + 2 Thermal
Photochemical Dis
Con

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I have a question about this problem involving mechanisms and drawing curved arrows for acids and bases. I know we need to identify the nucleophile and electrophile, but are there different types of reactions? For instance, what about Grignard reagents and other types that I might not be familiar with? Can you help me with this? I want to identify the names of the mechanisms for problems 1-14, such as Gilman reagents and others. Are they all the same? Also, could you rewrite it so I can better understand? The handwriting is pretty cluttered. Additionally, I need to label the nucleophile and electrophile, but my main concern is whether those reactions differ, like the "Brønsted-Lowry acid-base mechanism, Lewis acid-base mechanism, acid-catalyzed mechanisms, acid-catalyzed reactions, base-catalyzed reactions, nucleophilic substitution mechanisms (SN1 and SN2), elimination reactions (E1 and E2), organometallic mechanisms, and so forth."

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